This invention relates generally to systems for administering parenteral fluids to a patient, and, more particularly, to systems of this type having an infusion apparatus for infusing the fluid into the patient's vascular system.
Systems of this particular type have enjoyed widespread usage in hospitals for administering parenteral fluids at precise rates. The systems are useful for both venous and arterial infusions and typically include an infusion pump and an associated controlling device for pumping the parenteral fluid through a fluid tube and needle to the patient's vein or artery.
One drawback to conventional infusion pump systems of this type is that the needle can sometimes become dislodged from the patient's vein or artery. This will normally cause an increase in back pressure, but the pump will nevertheless continue to pump fluid at substantially the same fixed rate. The fluid therefore can infiltrate into the patient's body tissue and cause severe damage. Similarly, the needle can sometimes become dislodged from the patient entirely, yet the pump will continue to pump the fluid at the same fixed rate.
One known prior technique for detecting fluid infiltrations is to monitor the patient's skin temperature in the vicinity of the needle. Since the parenteral fluid is ordinarily cooler than the patient's body temperature, and since the fluid is not carried away as rapidly when an infiltration occurs, an infiltration will ordinarily create a temperature drop in the vicinity of the needle. Thus, whenever a drop in skin temperature is detected, it is deduced that an infiltration is occurring. This technique is not believed to have proven completely satisfactorily in all circumstances, such as, for example, when the parenteral fluid has a temperature substantially the same as that of the patient's blood.
Other known prior techniques for detecting an infiltration of a parenteral fluid into a patient's body tissue involve intervention by hospital personnel. In one such technique, an attendant visually inspects the region around the needle, to detect any swelling that might indicate an infiltration. In another technique, useful only when the fluid is being administered from a bottle under the force of gravity, the attendant periodically lowers the bottle to an elevation below the needle such that fluid flows outwardly from the patient. If when this is done the patient's blood does not appear in the fluid tube, it can be deduced that the needle is not in fluid communication with a vein or artery. Neither of these techniques has proven to be entirely satisfactory, one reason being that they both require the presence of trained hospital personnel and cannot be performed automatically.
Still another prior technique for detecting infiltrations and other fault conditions is used in a parenteral administration system that regulates flow rate using a pinch valve located in the fluid tube, between a drop chamber and the patient. In particular, the pinch valve is controllably adjusted in order to maintain the frequency of fluid drops into the drop chamber at a selected value. If the limits of the pinch valve are exceeded in attempting to maintain the selected drop frequency, it is deduced that a fault condition is present. Operator intervention is still required, however, in order to determine the particular type of fault condition, e.g., an infiltration, that is present.
A complete dislodging of the needle from the patient, such that the fluid is directed onto his skin, bedding, etc., is ordinarily detected only through a visual inspection by a hospital attendant. Such active participation by hospital personnel is not believed to be an entirely satisfactory solution to this problem.
It should be appreciated from the foregoing that there still is a need for an effective method and apparatus for automatically detecting faults such as infiltrations or an open line in a parenteral administration system of the type having an infusion device. The present invention fulfills this need.